1. Field of the Invention
The present invention relates to a semiconductor laser with a distributed Bragg reflector (hereinafter, referred to as "DBR") having an oscillating wavelength of 1.55 .mu.m, and more particularly to a semiconductor laser with a super structure grating (hereinafter, referred to as "SSG") DBR capable of generating a pulse train of from several hundred GHz (Giga Hertz) to several THz (Tera Hertz).
2. Description of the Prior Art
From a pulse generating semiconductor laser functioning as a light source of an optical communication network or an optical memory device, to generate a stable pulse train having a high repetition rate, it is profitable to use an integrated cavity semiconductor laser constituted by four main sections: a saturable absorber section, a gain section, a phase control section and a DBR section. In this laser, when a current signal greater than a threshold oscillation current necessary for operation thereof is applied thereto, a pulse train is generated by a harmonic passive mode locking (disclosed by S. Arahira et. al., IEEE Photon. Technol. Lett. 5, 1362, 1993).
A reflection factor of a limited length is vibrated in accordance with a wavelength, and thereby the harmonic passive mode locking occurs around a main oscillation wavelength.
It has been disclosed that a DBR structure using a grating plate having repetition rate of 120 .mu.m is used as one of DBR structures as well-known in the art. In the DBR structure, if the reflection factor is deviated by about 5 nm from a main oscillation wavelength (1560 nm), the amplitude of the oscillation curve is reduced about a half. Then, during occurrence of the harmonic passive mode locking, it is difficult to obtain a stable pulse train having an average output of several tens meW. The DBR having the above-mentioned characteristics is not preferably to apply to an ultrafast information communication network system.